Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Cash flows from operating activities:
Net income	$ 194.1	$ 178.7
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of property and equipment	9.8	11.6
Stock-based compensation	15.1	13.8
Investment Income, Amortization of Discount	(7.0)	(4.0)
Other Noncash Income (Expense)	(1.0)	(1.1)
Changes in operating assets and liabilities
Other assets	(4.1)	1.9
Accounts payable and accrued liabilities	(8.0)	12.1
Deferred revenues	38.6	41.8
Deferred Income Taxes	17.8	2.0
Net cash provided by operating activities	257.3	259.0
Net Cash Provided by (Used in) Investing Activities [Abstract]
Proceeds from maturities and sales of marketable securities	658.0	562.0
Purchases of marketable securities	(157.8)	(146.5)
Purchases of property and equipment	(3.8)	(5.7)
Net cash used in investing activities	496.4	409.8
Cash flows from financing activities:
Payments for Repurchase of Common Stock	269.9	230.5
Proceeds from employee stock purchase plans	8.3	8.0
Net cash used in financing activities	(261.6)	(222.5)
Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	(0.4)	(0.2)
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect	491.7	446.1
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, beginning of period	245.5	379.0
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, end of period	737.2	825.1
Supplemental cash flow disclosures:
Cash paid for interest	13.1	13.1
Cash paid for income taxes, net of refunds received	$ 16.1	$ 18.3